1. Field of the Invention
The present invention relates to a method of providing a handover service to a mobile communication terminal that is capable of multi-modal communication, and a mobile communication terminal for performing the method. More particularly, the present invention relates to method of eliminating an interruption of a data transmission service occurring during a handover between different communication networks, and a mobile communication terminal for performing the method.
2. Description of Related Art
Developments in wireless communication networks currently create a need for constant development of communication networks. Different communication networks with diverse characteristics, such as a cellular-based mobile communication network starting from an analog method and developing to a digital method, a wireless broadband Internet (WiBro) communication network providing a high-speed data service, a wireless local area network (WLAN), a wireless private area network, and the like are overlapping, and provide users with more diverse communication services.
Also, a mobile communication terminal constantly and functionally develops along with developments of the communication networks, and accordingly may provide diverse services in each similar communication network. Also, a multi-modal mobile communication terminal providing a service in the different communication networks is developing. A multi-modal terminal has a plurality of wireless interfaces, and a connection capability with various wireless communication networks.
A vertical handover (VHO) process from a first communication network to another communication network is required so that the multi-modal mobile communication terminal may smoothly provide service during a transition between the different communication networks. However, since communication network characteristics such as load, transmission environment, system, and the like, vary according to each communication network, a communication disconnection occurring during a handover may cause more complex and serious problems than in a single communication network.
FIGS. 1 through 4 are diagrams illustrating existing handover processes between different wireless communication networks.
Since a multi-mode mobile node (MN) includes at least one interface, the MN implements communication by connecting with a wireless communication network corresponding to a mode for each interface.
Referring to FIG. 1, the MN connects with a first wireless access network (AN1), and connects with a corresponding node (CN) via a first backbone network (BN1).
In this instance, a need for a VHO from a present wireless communication network to another wireless communication network may be generated due to diverse reasons. As an example, a handover may occur when the MN is removed from a region being covered by the AN1 to a region being covered by a second access network (AN2) as in a case of changing the MN's location, or when switching to another wireless communication network is required to control power usage of the MN. Another instance is when an appropriate communication network is selected according to the type of user-desired communication service, and a handover to a selected communication network is required.
As illustrated in FIG. 2, when a MN determines a handover from the AN1 to the AN2, the MN releases an association with the AN1, and transmits a request message for a handover registration via the AN2. The request message for the handover registration may include MN identification information identifying the MN, MN location information (for example, an Internet Protocol (IP) address), and the like, and is used as a message for the MN to register variations to an individual's location in a network. FIG. 2 illustrates a binding update message (BU) according to a standard of a mobile IP as an example of the request message for the handover registration.
A request message for a handover registration is transmitted (referring to FIG. 3) to a CN via a second backbone network (BN2), and the CN transmits a response message (referring to FIG. 4) to a request for the handover registration, i.e. a BU acknowledgement (BU_ACK) to an MN via an AN2, and thereby informs the MN that the CN normally identifies (or receives) the request for the handover of the MN. FIG. 4 illustrates a BU_ACK according to a mobile IP standard as an example of a response message to the request for the handover registration.
As illustrated in FIGS. 2 and 3, while the MN determines the handover and a request message for the handover registration is transmitted to the CN via the AN2 and the BN2, the CN transmits data through the BN1 and the AN1. Accordingly, this method does not allow the data transmitted via the AN1 to be received at the MN and is lost.
FIG. 5 is a diagram illustrating a flow of transmitting and receiving a message related to a handover between a CN and an MN according to a period of time, according to an existing method.
Referring to FIG. 5, the CN transmits data, while maintaining an association with a first interface (IF1) of the MN in time t0. When the handover is determined, the MN switches an association from an AN1 to an AN2 in time t1. In this instance, a second interface (IF2) transmits a request message for a handover registration (BU) to the CN via the AN2. In time t2, the CN receives the request message for the handover registration (BU) and stops data transmission to the IF1. Also, a response message to a request for the handover registration (BU_ACK) is transmitted to the IF2 via the AN2 in response to receiving the request message for the handover registration. The IF2 of the MN receives the response message to the request for the handover registration (BU_ACK) in time t3.
In FIG. 5, before the CN receives the request message for the handover registration (BU) from the MN, i.e. before time t2, the CN continuously transmits the data to the IF1 via the AN1. Accordingly, from a point in time when the MN determines the handover to a point in time when the CN receives the request message for the handover registration (BU), i.e. for a period of time of t0-t2, the MN may lose the data transmitted from the CN via the AN1.
As a conventional art to restore the data of a period of time of t0-t2, an existing method buffers and then forwards the data (a packet) transmitted from the CN to a node existing in the AN1 (for example, an access point (AP) or a router). Thus, the method is disadvantageous in that an additional function supporting the VHO is required to embody in the communication network.
Accordingly, a need exists for new technology to solve the problems of the conventional art in the process of performing a handover in an environment where different communication networks are distributed, and efficiently provide for seamless data service.